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'[EE]: URGENT Power Control help needed'
2001\02\16@064134 by Andy Faulkner

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Has anyone got a complete working circuit for
controlling the speed of a 240V AC electric motor such
as a hand drill from a low dc voltage say 0 to 12V or
0 to 5V.

I need one urgently for a show were doing this
weekend.

Andy Faulkner





=====

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Pyrosync International http://www.pyrosync.co.uk

Tel +44 778 896  6087.....................UK Dial 0778 896 6087

Fax +44 870 132 3275.....................UK Dial 0870 132 3275
http://www.event-supplies.co.uk http://www.spectacular-fireworks.co.uk


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2001\02\16@093918 by Chris Eddy

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Andy;

The design that you are looking for is very complicated and will likely
take custom magnetics and PCB designs.  I doubt if you will get it built
by this weekend.

The fastest path is to go buy a UPS (an inverter is even better, but not
in store), preferably one that works on a single 12V battery (assuming
that you have 12VDC), then splice into the battery wires.  Then overnight
two items... a 120/240 stepup transformer, and a 240VAC VFD.  Keep your
checkbook and credit cards handy.

G'luck
Chris Eddy~

Andy Faulkner wrote:

{Quote hidden}

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2001\02\16@112742 by Bob Blick

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<crude_solution>
How about using a lamp dimmer, replacing the pot with a CDS photocell, and
illuminating that with a light bulb or LED? You should be able to get all
that at Radio Shack or your local equivalent.
It'll be nonlinear, but I imagine you have a PIC in there somewhere that
will linarize it.
</crude_solution>

Cheers,

Bob


On Fri, 16 Feb 2001, Andy Faulkner wrote:

{Quote hidden}

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2001\02\16@160622 by jhancock

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You might consider building an emitter follower circuit and using a
potentiometer in the base to control the base voltage.  I don't know how
that would work with an AC motor.  I used something like that on an old auto
dc fan motor to get a variable speed control - worked OK.

+12VDC source would go the (NPN) collector and the emitter to the motor.
Other motor lead goes to -12V.  The power potentiometer (I used 1000 ohms
several watt rated potentiometer) was connected from +12V to -12V with the
wiper going to the base of transistor.  This would provide a variable output
voltage between zero and about 11.3 volts.  Actually, I used two transistors
in parallel, a couple old obsolete 2N274 PNP types (polarity reversed from
above).  You can get a NPN (I think) 2n3055 power transistor at Radio Shack
which is good for several amps if heat sinked.  If you don't want the full
voltage range, put a resistor between +12 V and the top of the potentiometer
to limit the maximum base voltage.

You need to mount the power transistor on a heat sink - I used scrap
aluminum or aluminum chassis or sheet of copper pcb.

An IRF 510 mosfet also available at RS might also work and would not draw
base current allowing a smaller power rated potentiometer.  Not sure how the
output voltage would vary with gate voltage.

Jess
{Original Message removed}

2001\02\16@163913 by Eisermann, Phil [Ridg/CO]

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no, you can't control an AC motor with a single transistor that way. you'd
need several in a bridge configuration. There are actually special power
bricks made for this (e.g POWEREX). And don't forget, he's asking for a 240V
AC motor! There's factor of sqrt(2), not including any transients. At a bare
minimum, you'd need a 600V device for this. So i guess the 2N3055 is right
out... so is the IRF511 from radio shack (which is rated at 80V).

{Original Message removed}

2001\02\16@172241 by David VanHorn

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>
>You might consider building an emitter follower circuit and using a
>potentiometer in the base to control the base voltage.  I don't know how
>that would work with an AC motor.  I used something like that on an old
>auto dc fan motor to get a variable speed control - worked OK.

Likely to get REALLY hot.
AC motors aren't designed to be speed controlled, except by altering the
drive frequency (within limits)


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2001\02\16@173042 by jhancock

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I would agree if it is a true "ac" motor that the emitter follower will not
work.  If it is an ac/dc motor it may work.  If it requires 240 vac to run,
then getting that from a 5 or 12v source is doubtful within the time frame.
Simpler to go to Sears (or equivalent) and purchase a battery driven
handheld variable speed drill.  The actual requirement was not specified so
don't know if that would serve or not.

In any case - good luck!

Jess

{Original Message removed}

2001\02\16@173310 by Bob Blick

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> Likely to get REALLY hot.
> AC motors aren't designed to be speed controlled, except by altering the
> drive frequency (within limits)

The original post said "hand drill motor", so that would suggest universal
motor. A lamp dimmer will work fine, that's basically what's in the
trigger speed control(can substitute a CDS photocell for the trigger
potentiometer!).

-Bob

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2001\02\16@174954 by David VanHorn

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>
>The original post said "hand drill motor", so that would suggest universal
>motor. A lamp dimmer will work fine, that's basically what's in the
>trigger speed control(can substitute a CDS photocell for the trigger
>potentiometer!).

Ok, that's what I'd try in that situation then.

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2001\02\16@180046 by Eisermann, Phil [Ridg/CO]

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Well, if you're saying its a universal motor, you could use phase-control.
But I'm confused on how would you do this with an emitter-follower. Or are
you proposing rectifying the AC voltage first, and then using the
emitter-follower to limit the drive current? I've seen this done with a
thyristor.

I guess we need to have the original poster specify what kind of AC motor
was meant. But if he wants it by this weekend, it's probably too late :(

{Original Message removed}

2001\02\16@181906 by jhancock

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The emitter follower suggestion assumed the motor was ac/dc type.  The
original post wanted to run from a variable 5 v or 12 v dc source.

Whether this would work certainly depends on the motor.  The light dimmer
may work on ac, but on dc I think it would stay on once turned on (if it
would turn on) and apply dc to the motor.  Even if the motor is ac/dc it is
questionable if a LV dc would run it - depends on the motor.

Anyway Andy, let us know what you ended up doing.

Jess


{Original Message removed}

2001\02\16@215454 by steve

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> I guess we need to have the original poster specify what kind of AC motor
> was meant. But if he wants it by this weekend, it's probably too late :(

From the "if you can't fix it with a hammer, it isn't worth fixing
dept", why not buy a drill speed controller from the hardware store,
rip out the pot and replace it with a motorised pot from an
electronics store. You may need to adapt your pot into the
motorised one as it will be the wrong value and a log type.

Alternatively, a couple of belts and pullies from a VCR repair kit, a
hobby servo and a tube of 5 minute epoxy.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
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2001\02\16@235127 by Tom Messenger

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At 05:19 PM 2/16/01 -0500, you wrote:
>
>Likely to get REALLY hot.
>AC motors aren't designed to be speed controlled, except by altering the
>drive frequency (within limits)
>
>--
>Dave's Engineering Page: http://www.dvanhorn.org
>Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9
>

Like Dave said, REALLY hot.

About 5 years ago, an architecture student at CSU-San Luis Obispo (aka Cal
Poly), set up a demo for open house day.  In a room full of little houses
and buildings made of cardboard and stuff, his setup used an AC powered
drill to simulate earthquake vibrations.  To run slow enough, he powered it
up through a standard lamp dimmer - triac kind of thing. It ran hot.  No
one turned off the power at the end of the day. It ran on and on for a
while. Then it caught fire.  Then the cardboard building caught fire. Then
somewhere around $10,000,000 worth of science building burned up. Yup;
there was a film at 11...

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2001\02\17@005105 by Bob Blick

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>If it's an ac motor or a universal motor running on AC, you
>can't control it via a single transistor.

Hi Phil,

Don't tell that to Ampex then, because I've worked on 24-track Ampex MM1200
tape recorders that did just that.

They used a bridge rectifier with the DC side hooked to a transistor. The
AC side of the bridge was in series with the motor and the 110 VAC. The
transistor was driven by a simple circuit that used an optoisolator, so the
whole thing was DC controlled and isolated.

It did require large heatsinks but was smooth and quiet and could move tape
pretty well.

That stuff is ancient history and I barely remember it, but thought it was
cool for its simplicity. The motors I believe were AC capacitor-run,
similar to ones Ampex used in the relay-operated MM1100(which had big
resistors for different torque levels).

Cheerful regards,

Bob Blick

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2001\02\17@060920 by Peter L. Peres

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>How about using a lamp dimmer, replacing the pot with a CDS photocell,
>and illuminating that with a light bulb or LED? You should be able to get
>all that at Radio Shack or your local equivalent. It'll be nonlinear, but
>I imagine you have a PIC in there somewhere that will linarize it.

The LED + LDR solution is very linear over most of the range.

Peter

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2001\02\17@091259 by Roman Black

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Bob Blick wrote:
{Quote hidden}

Thanks Bob, thats cool. So that was a linear setup
for AC with one transistor! I dig it. :o)
-Roman

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2001\02\19@071601 by Andy Faulkner

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Sorry Guys,

I think I confused the matter a little with the 12V.

The AC Motor is brushless and phase control should
work from what I know so far, a lamp dimmer appears to
be the best solution but I needed a ready made circuit
that could be incorporated into an existing design
quickly, we did indeed end up using a lamp dimmer
capable of controlling a 100W bulb, and had to adjust
this manually.

Has anyone got a design that could control flood
lights 500W to 1000W used outside security lights, the
ones used in the back garden with a PID.

We can supply a variable control voltage from 0 to 12V
in 16Bit steps but this will only source a few hundred
milliamps.

Thanks for your help so far

Andy Faulkner



=====

Andy Faulkner EraseMEandyf97spam_OUTspamTakeThisOuTyahoo.com
Pyrosync International http://www.pyrosync.co.uk

Tel +44 778 896  6087.....................UK Dial 0778 896 6087

Fax +44 870 132 3275.....................UK Dial 0870 132 3275
http://www.event-supplies.co.uk http://www.spectacular-fireworks.co.uk


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2001\02\20@085049 by Eisermann, Phil [Ridg/CO]

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       So the motor current returned/was fed through the bridge, where it
could be controlled via a transistor? That's pretty clever! I would have
never thought of it.

       I stand somewhat corrected. You can control it with a transistor, if
you rectify the AC somewhere in there.

{Original Message removed}

2001\02\21@023309 by Michael Rigby-Jones

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> -----Original Message-----
> From: Eisermann, Phil [Ridg/CO] [SMTP:@spam@peisermaKILLspamspamRIDGID.COM]
> Sent: Tuesday, February 20, 2001 1:46 PM
> To:   KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: URGENT Power Control help needed
>
>         So the motor current returned/was fed through the bridge, where it
> could be controlled via a transistor? That's pretty clever! I would have
> never thought of it.
>
>         I stand somewhat corrected. You can control it with a transistor,
> if
> you rectify the AC somewhere in there.
>
>
I built a variable AC supply many years back using this method, a 230:15
transformer with the 15v secondary coupled to the 15v secondary of an
identical transformer, via a bridge and a 2N3055 transistor.  A voltage
divider, rectifier, and a 741 opamp stabilised the voltage.

Mike

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